Method for producing paper



March 5, 1963 HORNBOSTEL ETAL 9,

METHOD FOR PRODUCING PAPER Filed Feb. 20, 1959 he ILZZLT'S L/oyd Hornbosfe/ 5 rw 0d [fa/f atetit 3,979,799 Patented Mar. 5, 1963 Wis., a corporation of Wisconsin Filed Feb. 20, 1959, Ser. No. 794,594 2 Claims. (CI. 34-41) This invention relates to a method for producing paper. More particularly, this invention relates to a method of drying a wet paper web to produce grades of paper with improved suitability for coating and printing.

As a rule, machine glazed papers (commonly called MG paper) are made in a Yankee dryer machine or Yankee machine. Such a machine may have a cylindrical or Fourdrinier wet end and it may also have a number of presses or auxiliary dryers of the usual type. The characteristic feature of the Yankee machine is the large Yankee dryer drum, having a diameter of from about 9 feet to about 15 feet, which is made of cast iron or steel and has a very high polish imparted to the outside cylindrical surface. Soft material, such as a paper web, will develop a fine glazed smooth surface if it is pressed against the heated finely polished dryer drum surface and retained thereon during the drying of the web. Such Yankee dryers have normally been used singly. For tissue and other light-weight papers the web is removed from the dryer by a creping doctor. Machine glazed or MG papers are dried completely on the single Yankee and released easily when so dried. Numerous attempts have been made to use more than one Yankee dryer in succession. Where these combinations have been usable at all, however, they have relied upon special features to obtain the release of partly dried web or have not been intended to distribute the drying action more or less equally between each of the plurality of machines.

We have discovered that a web of moderateweight will release from the surface of a Yankee dryer at moisture contents as low as 65% bone dry, although the customary glaze is partly or entirely lost. It has been found that the glazing of the web which is customary on one side only in the MG sheet is actually a dual effect. The surface fibers of the web are in fact coalesced due to the action of the usual pressure or sticker roll and to the adherence to the polished sur ace of the dryer. This forces the fibers into the interfiber voids and causes one side of the web to take the shiny glaze like the dryer surface. When this Web is removed less than fully dried, the surface gloss is lost. However, the smoothing and leveling effect remains and enough moisture may be left in the web to permit its being recast on the opposite side against a second dryer to complete the drying process and provide a glazed surface on this second or opposite side.

it is therefore an object of this invention to provide a method of producing a web of paper having an unusually smooth surface on two sides and also having improved uniformity of density and opacity such that it may be coated by using a minimum amount of coating material to produce publication grades of paper having lighter weight for equal or improved performance.

It is a further object of this invention to provide such a method of producing such grades of paper having improved appearance and printability.

It is a still further object of this invention to provide such a method of producing such publication grades of paper which will afford characteristics which permit the use of lighter weight paper than has heretofore been possible in order to achieve lower cost in paper, postage and delivery.

It is a further ob ect of this invention to provide an improved method of drying paper.

Briefly, in accordance with one aspect of the invention, the wire side of a moist newly formed web of paper is cast on a first smoothly polished and preferably heated metallic surface and maintained thereon until it is not more than bone dry. The web is then removed from the first surface, conveyed to a second similar surface, and the opposite side of the web recast againstthe second surface preferably by the use of a roll or belt comprising material to which the web will not adhere. The web is maintained against the second surface until it reaches approximately commercial dryness which is generally considered to be 92-96% bone dry.

Other objects, features, and advantages ofthe present invention will be more fully apparent to those skilled in the art from the following detailed description taken in connection with the accompanying drawing in which like reference characters refer to like parts throughout and wherein:

The single FIGURE of the drawing is a diagrammatic view of a paper machine suitable for carrying out the method of the present invention.

In the drawing there is diagrammatically illustrated the operation of a paper machine utilizing two Yankee dryers to carry out the method of the present invention. A web of paper may be formed on a conventional Fourdrinier wire it or by any other convenient means. The web is picked up by a conventional pick up felt 11 and carried through a press couple 12. The web will e of normal moisture content, that is, from 25% to 35% bone dry. The web after leaving press couple 12 is cast on a first Yankee dryer drum 13 by a conventional sticker roll 14. Suitable rollers 15, 15 and 17 may be provided over which the felt 11 is trained in an endless loop feeding it through the Fourdrinier wire 10, the press cou' ple 12, and the sticker roll 14.

The web 18 is preferably carried for about of a rotation by the clockwise rotation of the Yankee dryer drum 13 as indicated by the arrow above the drum in the drawing. The Yankee dryer drum may be of the conventional type described above and is provided with conventional heating means not shown in the drawing and with a hard polished preferably metallic surface. As is apparent from the drawing, the wire side of the web 18 is initially cast on drum 13 by the sticker roll 14.

At point 19 the web is pulled from the surface of drum 13 and trained over a roll 20 at a moisture content less than 80% bone dry. The desired moisture content may, of course, be achieved for any given web by suitably seleoting the size and speed of rotation of the dryer drum and by adjusting its temperature. The angle which the portion of the web between point 19 and roll 20 makes with a tangent to the dryer drum at the point 19 will depend upon the actual moisture content chosen and to some extent, on the kind of pulp stock furnished to the forming wire 10. Obviously, the greater this angle is (the higher the moisture content) the more damage will be done to the surface of the web. However, the loss of the specular gloss from the wire side of the web in leaving the first dryer drum 13 is not significant so long as the surface remains smooth.

The web is transferred from roll 29 in a short open draw to a belt 21 which is trained in an endless loop over a pressure roll 22 and suitable guide rolls 23, 24, 25 and 26. The belt 21 may be of any relatively thin material having a smooth surface and requires only that one side at least be of an inactive material, suchas one of the synthetic resinous polymers commonly known as Teflon, so that the web will not adhere to it in passing through the nip 28 between pressure roll 22 and the second Yankee dryer drum 29.

loop so that it supports or urges the web 18 against the surface of the dryer drum 29 during the counter-clockwise rotation of the dryer drum.

At point 37, the web is removed from dryer drum 29 and is trained over a suitable guide roll 38 to be fed to apparatus for calendering the upper in any conventional manner if required and is then wound into suitable commercial rolls. When the paper leaves the second dryer drum at point 37, the paper is at commercial dryness or approximately 4% to 8% moisture (92-96% bone dry).

It may be desirable, alternatively, to use only the pressure roll 22 forming the nip 28 with the dryer drum 29 and to omit guide rolls 26 and 27. Under certain circumstances it may also be desirable to heat the belt 34} in order to improve its release qualities. In addition to synthetic resinous materials, the belt 21 can also be of any fairly hard material such as rubber or steel.

It will, of course, be understood that the surface speed of rotation of the second Yankee dryer drum 29 must be substantially the same as that of the first drum 13. However, either the diameter of the drum 29 or the temperature at which its surface is maintained may be varied to achieve the desired drying etfect which will reduce the moisture content of the web from that at which it is cast onto the drum at nip 28 to the desired commercial drynes's value at point 37.

It is thus seen that by first casting the wire side of a web of paper onto a first Yankee dryer drum and maintaining the web thereon until the moisture content is reduced so that the paper is from 65 to 80% bone dryand then releasing the web from the surface of the first drum and recasting the opposite side of the web onto a second drum on which it is maintained until the web reaches commercial dryness, a web of paper maybe produced which has an unusually smooth glazed surface on the side which was in contact with the seconddryer drum and which (by virtue of the effect of the first dryer drum) has improved uniformity of density and opacity.v These qualities permit coating of this paper by using less coating material than has heretofore been required. The method also produces publication grades of papers having lighter weight for equal or improved performance and having improved appearance and printability. This, in turn, permits the use of. lighter weight paper to achieve the same quality of printed matter which in turn results in lower initial paper cost and in reduced postage and delivery costs.

While a particular exemplary preferred embodiment of the present invention has been described in detail above, it will be understood that modifications and variations therein may be effected without departing from the true spirit and scope of the-novel concepts of the invention as defined by the following claims.

We claim as our invention:

1. A method of drying a wet castable paper. web that comprises casting a moist newly formed web having a wire side so that the wire side is disposed on a smoothly polished heated metallic traveling surface, maintaining the web against said surface until it is from to bone dry, removing the Web from the first surface, conveying the web to a second similar surface, recasting the opposite side of the web against the second surface by urging the web against said second surface with a member comprising a material to which the web will not stick, and continuing the web on the second surface until it is dewatered to 92-96% dryness.

2. A method of drying a wet castable paper web that comprises casting a moist newly formed web on a smoothly polished heated metallic traveling surface, maintaining the web having a Wire side so as to dispose the wire side against said surface until it is from 65% to 80% bone dry, removing the web from the first surface, conveying the web to a second similar surface, re casting the opposite side of the web against the second surface by urging the web against said second surface with a member comprising a material to which the web will not stick, and continuing the Web on the second surface until it is dewatered to 9296% dryness.

References Cited in the file of this patent UNITED STATES PATENTS Re. 21,098 Carroll Mar. 30, 1939 2,537,129 Goodwillie Ian. 9, 1951 2,611,974 Stratveit Sept. 30, 1952 FOREIGN PATENTS 233,493 Great Britain May 14, 1925 

1. A METHOD OF DRYING A WET CASTABLE PAPER WEB THAT COMPRISES CASTING A MOIST NEWLY FORMED WEB HAVING A WIRE SIDE SO THAT THE WIRE SIDE IS DISPOSED ON A SMOOTHLY POLISHED HEATED METALLIC TRAVELING SURFACE, MAINTAINING THE WEB AGAINST SAID SURFACE UNTIL IT IS FROM 65% TO 80% BONE DRY, REMOVING THE WEB FROM THE FIRST SURFACE, CON- 